The invention relates to an electric motor with a stationary and a movable active motor part, one of the two active motor parts comprising a motor winding and the other a motor magnet, an air gap being formed between said active motor parts, while the motor winding is built up on a synthetic resin carrier foil and is formed through local removal of copper material with which the synthetic resin foil had previously been fully coated.
The invention further relates to a hard disk drive provided with said electric motor.
EP 410 293 B1 discloses an electric motor in which a permanent magnetic hollow cylinder is arranged on a central shaft fixedly connected to a rotatable hub. The permanent magnetic hollow cylinder is surrounded by a metal plating stator which is arranged on a stationary base part. The stator has a coil winding inserted into slots of the stack of iron laminations. The bearing of the hub is provided radially and axially by means of hydrodynamic bearings.
The interaction between the slotted stator and the multipole magnetized permanent magnets causes so-called detent torques. These are moments of torque which change periodically with the disk rotation, whose average value is zero, and which accordingly do not contribute to the nominal torque. The retentive moments cause acoustic noises, mechanical vibrations, and rotation speed fluctuations; in addition, they increase the required initial torque, which is a critical quantity particularly for hard disk drives.
The manufacture of planar motor windings is known, whereby copper tracks provided on synthetic resin foils are so etched that only planar coil windings remain. Such motor windings are capable of perfect operation and present no problems as long as the foils are not bent.
Problems do arise, however, when such a winding is shaped into a cylinder. Then the otherwise simple technology leads to short-circuits between the conductor tracks. In addition, such windings cannot be made sufficiently round. This means that unnecessarily wide air gaps must be created. The exact motor rotation is impaired thereby. These problems arise especially in small motors which are used for hard disk drives.